Current design practice for designing synchronous belt drives follows the same general principles used for designing inverted tooth chain drives wherein the chain (or belt, as the case may be) teeth carry the load imposed on the drive. However, a belt differs from a chain in at least two important respects, i.e., belts, because of their construction of elastomeric material, usually with a reinforcing cord and/or cloth covering, elongate much more than chains under load; and the resilient belt teeth deflect much more than the relatively rigid teeth of a chain. In a belt drive, friction between the belt and the pulley peripheries can be utilized to carry a major portion of the load.